Reading it, though, I wonder if the business model of "write a new popular game once a month" will go. As someone who's worked at that pace in the past (and occasionally now), I can confirm that the well of great ideas will run dry. You can't just throw away designs when you're working on such a schedule. If you're 85% done with a game and it's only moderately interesting, then your only choices are to do some minor tweaks with the hopes that it'll get marginally better, or dump the idea and move on.
Of course, if you had several teams (perhaps three) each working on a game, you'd have a little buffer and some more "tweak time" to make a somewhat-fun game into a really-fun game. Of course, making your company into something that can support three teams requires a lot of cash. You have to have a good eye.
Desktop Tower Defense, though, is a pretty good idea. It's got appeal to the RPG-wargame crowd, but it's uninvolving enough that it can be played casually.